Hepatitis C virus infections affect approximately 2% of the worldwide population. The virus has a high propensity for inducing persistent infections that over time progress to serious liver disease including cirrhosis and liver cancer. HCV is the leading cause of liver transplantation in the US today. Research on HCV has been impeded by the lack of a small animal model and a tissue culture system. GBV-B is the virus phylogenetically most closely related to HCV and it causes hepatitis in tamarins. We have developed the GBV-B animal model as a surrogate small primate model for HCV. We have recently demonstrated that the common marmoset is equally permissive for GBV-B infections and is the preferred animal model for a number of reasons. In addition, we have developed a robust tissue culture system for GBV-B utilizing primary hepatocyte cultures from tamarins or marmosets. In this proposal, we will more fully develop the animal and culture models for GBV-B and test specific hypotheses relevant to HCV diseases. The specific aims are the following: 1) to better characterize the animal model with regard to the pattern of viral infection, host gene expression in the liver, and the resulting immune response to infection. Specific hypotheses will be tested with regard to the factors limiting the spread of infection in the liver and the events preceding viral clearance; 2) to use lentivirus based gene therapy to examine the role of type 1 and type 2 interferons in the initial spread of the infection in the liver and the elimination of infected hepatocytes; 3) to use adoptive T cell transfer to examine the role of CD4+ and CD8+ T cells in viral clearance; and 4) to more fully develope the tissue culture system. Although the tissue culture system will be utilized in most of the aims in this proposal, in the final aim, we will attempt to improve the technology with regard to the use of lentiviral vectors to define receptor interactions, applications in reverse genetics, isolation of immortalized cell lines permissive for GBV-B and modulation of liver gene expression by GBV-B. [unreadable] [unreadable] [unreadable]